In internal combustion engines, catalyst aging and deterioration is a serious concern. Such degradation may cause engines to fall out of emissions compliance. Conventional catalyst maintenance includes periodic replacement of the catalyst or the catalytic converter after a given period of time. Periodic replacement may be costly and wasteful in cases where the catalyst may have useful life remaining.
Attempts have been made to monitor catalyst deterioration in order to determine when a catalyst is no longer useful. Such conventional attempts to monitor combustion engine catalyst deterioration have strictly been based on comparing time lag between signals from upstream and downstream oxygen sensors such as lambda sensors.